On capturing the grain-scale elastic and plastic anisotropy of alpha-Ti with spherical nanoindentation and electron back-scattered diffraction

Abstract

Spherical nanoindentation combined with electron back-scattered diffraction has been employed to characterize the grain-scale elastic and plastic anisotropy of single crystal alpha-Ti of two different compositions (in two different titanium alloys). Data analyses protocols needed to reliably extract the desired properties of interest are extended and demonstrated in this paper. Specifically, the grain-scale mechanical response is extracted in the form of indentation stressstrain curves for commercially pure (CP-Ti) alpha-Ti and alloyed (Ti-64) titanium from measurements on polycrystalline samples. The results are compared with responses of single crystals and nanoindentation tests (hardness and modulus) from the literature, and the measured indentation moduli are validated using crystal-elastic finite element simulations. The results obtained in this study show that (i) it is possible to characterize reliably the elastic and plastic anisotropy of alpha-Ti (hcp) of varying alloying contents with spherical nanoindentation stressstrain curves, (ii) the indentation modulus of alpha-Ti-64 is 5-10% less than CP-Ti, and (iii) the indentation yield strength of alpha-Ti-64 is 50 to 80% higher than CP-Ti.

High Throughput Assays for Additively Manufactured Ti-Ni Alloys Based on Compositional Gradients and Spherical Indentation

“…1 Schematic of the conventional approach (top row), and how this can be augmented with a high throughput (HT) approach (bottom row) to explore materials with different combinations of compositional and/or process conditions. Both tensile and indentation stress-strain curves are from previous work [7] 32], it was demonstrated that the following definitions meet these criteria…”

“…The indentation methods, because of their very small probe volumes and high throughput nature, are capable of quantifying the variances in the measured mechanical properties at both these scales. The potential benefits of these indentation techniques in extracting reliable process-structureproperty linkages have been demonstrated in a few recent studies [7,25]. Other currently available approaches suitable for mechanical characterization in small material volumes include microscale tension/bending tests [26,27] and micropillar deformation tests (produced by focused ion beam (FIB) milling) [28,29].…”

“…In this regard, it should be noted that the recently developed spherical indentation protocols [6,8] are capable of extracting indentation stress-strain (ISS) curves from very small volumes (indentation zone radii ranging from~50 nm to~500 μm). Significant progress is being made in correlating the properties measured in indentation with the properties measured in conventional testing such as simple compression [6,7,31,32], which will aid tremendously in increasing the interpretability of the indentation results.…”

“…They should also allow generalization for the elasticplastic indentation and produce meaningful indentation stressstrain curves with an initial elastic regime followed by transition into an elastic-plastic regime. In recent work [6,7,10, Fig. 1 Schematic of the conventional approach (top row), and how this can be augmented with a high throughput (HT) approach (bottom row) to explore materials with different combinations of compositional and/or process conditions.…”

“…In this regard, recent advances in spherical indentation stress-strain protocols [6][7][8][9][10][11][12][13] offer many advantages. The conventional practices in indentation testing rely on sharp indenters and analyze the unloading segments after imposing substantial amounts of indentation loads (or depths) to arrive at estimates of modulus and hardness [14][15][16].…”